Emulsion binders



Nov. 18, 1969 L. D. TAYLOR T L EMULSION BINDERS 5 Sheets-Sheet 1 Filed Jan. 27, 1966 l MICRON FIG.

l MICRON FIG.

INVENTORS PETER H. ROTH and LLOYD D. TAYLOR BROWN and MIKULKA ANN G. LEIBOWITZ ATTORNEYS Nov. 18, 1969 Filed Jan. 2'7. 1966 L. D. TAYLOR ET AL EMULSION BINDERS FIG. 4

5 Sheets-Sheet z I MICRON INVENTORS PETER H. ROTH and LLOYD D. TAYLOR BROWN on: MIKULKA ANN G. l: ElBOWlTZ ATTORNEYS Nov. 18, 1969 Filed Jan. 27. 1966 D. TAYLOR ET AL EMULSION BINDERS 5 Sheets-Sheet I l MICRON INVENTORS PETER H. ROTH and LLOYD D. TAYLOR BROWN (mg MIKULKA ANN G. IPEIBOWITZ ATTORNEYS Nov. 18, 1939 D. TAYLOR ETAL 3,479,186

EMULSION BINDERS Filed Jan. 27. 1966 5 Sheets-Sheet 4.

FIG. 7 IMICRON FIG. 8 lMlCRON INVENTORS PETER H. ROTH und LLOYD D. TAYLOR BROWN ung MIKULKA ANN G. L EIBOWITZ ATTORNEYS L. D. fAYLOR, ET AL 3,479,186

Nov. 18, 1969 EMULSION BINDERS 5 Sheets-Sheet 5 Filed Jan. 27, 1966 mzomoj zz INVENTORS PETER H. ROTH 0nd LLOYD D. TAYLOR BROWN and MIKULKA and ANN G LEIBOWITZ ATTORNEYS United States Patent Office 3,479,186 Patented Nov. 18, 1969 3,479,186 EMULSION BINDERS Lloyd D. Taylor, Everett, and Peter H. Roth, Needham, Mass, assignors to Polaroid Corporation, Cambridge,

Mass., a corporation of Delaware Filed Jan. 27, 1966, Ser. No. 523,379

Int. Cl. G03c 1/72 US. Cl. 96-114 10 Claims ABSTRACT OF THE DISCLOSURE A photosensitive silver halide emulsion wherein the emulsion binder comprises a copolymer of vinyl alcohol and vinyl pyrrolidone.

This invention relates to photography and, more particularly, to novel photosensitive photographic elements.

It is one object of the present invention to provide novel photosensitive emulsions.

Another object of the present invention is to provide methods of fabricating novel photosensitive emulsions.

A further object of the present invention is to provide certain novel silver halide emulsions wherein photosensitive silver halide crystals are disposed in specified synthetic polymeric binders, namely, vinyl alcohol/ vinyl pyrrolidone copolymers.

A still further object of the present invention is to provide specified photosensitive silver halide emulsions for employment in diffusion transfer photographic processes.

Other objects of the present invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties, and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims. 1

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIGURE 1 is an electron photomicrograph having a magnification of 40,000 showing silver halide crystals in an .emulsion binder comprising a vinyl pyrrolidone homopolymer;

FIG. 2 is an electron photomicrograph having a magnification of 40,000 showing silver halide crystals in an emulsion binder comprising a vinyl alcohol homopolymer;

FIG. 3 is an electron photomicrograph having a magnification of 40,000 showing silver halide crystals grown in one novel emulsion binder within the scope of this invention, comprising a vinyl alcohol/vinyl pyrrolidone copolymer having a molar ratio of 36 parts vinyl alcohol to 64 parts vinylpyrrolidone; I

FIG. 4 is an electron photomicrograph having a magnification of 40,000 showingsilverhalide crystals grown in: another novel emulsion binder within the scope of this invention, comprising a vinyl alcohol/vinyl pyrrolidone copolymer having a molar ratio of 57 parts vinyl alcohol to 43 parts vinyl pyrrolidone;

'FIG, 5 is an electron photomicrograph having a magnification of 40,000 x showing silver halide crystals grown in still another novel emulsion binder within the scope of this invention comprising a vinyl alcohol/vinyl pyrrolidone copolymer having a molar ratio of 75 parts vinyl alcohol to 25 parts vinyl pyrrolidone;

FIG. 6 is an electron photomicrograph having a magnification of 10,000X, showing silver halide crystals grown in still another novel emulsion binder within the scope of this invention comprising a vinyl alcohol/vinyl pyrrolidine copolymer having a molar ratio of 92 parts vinyl alcohol to 8 parts vinyl pyrrolidone;

FIG. 7 is an electron photomicrograph having a magnification of l0,000 showing silver halide crystals in an emulsion binder comprising a physical mixture of polyvinyl alcohol and polyvinyl pyrrolidone in a weight ratio of 70 parts polyvinyl alcohol to 30 parts polyvinyl pyrrolidone;

FIG. 8 is an electron photomicrograph having a magnification of 10,000 showing silver halide crystals in a novel emulsion binder within the scope of this invention comprising a vinyl alcohol/vinyl pyrrolidone copolymer having a molar ratio of parts vinyl alcohol to 25 parts vinyl pyrrolidone and totally devoid of gelatin in any form; and

FIG. 9 is a wedge spectrogram curve obtained when a novel emulsion within the scope of this invention is spectrally sensitized with a symmetrical benzothiazole carbocyanine dye.

Much effort has been expended in the past in attempts to replace gelatin as a colloid binder in photographic silver halide emulsions with suitable synthetic substances. However, despite the known disadvantages of gelatin (in particular, its variability, which in large measure results from variations in the raw materials from which it is prepared), to date, there have been found no synthetic materials which perform in a manner approximating gelatin in photographic processes and which possess most or all of its necessary characteristics as silver halide emulsion binder.

It is generally agreed that any substitute for gelatin as a photosensitive silver halide emulsion binder would have to fulfill at least the following basic requirements, as set out by Deryagin, B.V., and Levi, S.M., in Film Coating Theory, Focal Press, Inc., 1964, at page 113:

(a) Absence of (or constant) photographic activity.

(b) Ability to form an adsorption layer on microcrystals of silver halide permitting stable suspensions to be obtained.

(c) Ability to form adsorption layers as described in (b) above which do not prevent growth of silver halide micro-crystals (Ostwald ripening) during physical ripening.

(d) Solubility in water and ability to form a gel.

(e) Ability to form transparent, mechanically stable, heat-resistant, elastic emulsion layers which can be permeated by developing solutions. These properties should preferably be maintained at different temperatures, humidities, and other usage conditions.

(f) Miscibility with gelatin for use in partial substitution applications.

One synthetic material which has received wide attention as a possible gelatin substitute in photographic processes is polyvinyl alcohol. However, pure polyvinyl alcohol has been found to have certain properties which render it unsuitable for this purpose, one of the most significant of which is its tendency to behave as a silver halide crystal growth restrainer. Another synthetic material which in the past has been considered promising as a gelatin substitute is polyvinyl pyrrolidone, for the reason that it possesses many properties in common with polyvinyl alcohol but under certain conditions, will allow silver halide crystal growth. However, in order to achieve this effect, it is generally necessary to include an excessive amount of ammonia along with the polymer and under this circumstance, crystal growth usually proceeds in a manner uncontrollable in both rate and extent. Under neutral conditions, polyvinyl pyrrolidone has been found to inhibit silver halide crystal growth in a manner substantially identical to that of polyvinyl alcohol.

It has now been found that notwithstanding the undesirable features of vinyl alcohol and vinyl pyrrolidone homopolymers discussed above, all of the gelatin in photosensitive silver halide emulsions may be replaced with copolymers of vinyl alcohol and vinyl pyrrolidone. Such copolymers have unexpectedly been found to substantially meet all of the basic requirements for synthetic gelatin substitutes given above, as will be described in detail hereinafter. Moreover, the resulting emulsions are readily sensitized, and are characterized by excellent latent image stability and good to excellent film speed.

The vinyl alcohol/vinyl pyrrolidone copolymers contemplated by this invention may be characterized as having the following general formula:

wherein x is a positive integer. They are readily prepared by the hydrolysis, e.g., with alkoxides in alcohol solution, of corresponding vinyl pyrrolidone/vinyl acetate copolymers, which materials are generally readily available commercially. Preferably, the vinyl pyrrolidone/vinyl acetate copolymers from which the materials of this invention are prepared have a molecular weight range of from about 20,000 to 300,000. Vinyl pyrrolidone/vinyl acetate coplymers of this nature, in a variety of ratios, are commercially available from General Aniline and Film Co., Antara Chemicals, 435 Hudson Street, New York, N.Y., under the trade designation Kolinia Resins. If it is desired to synthesize these materials, procedures for copolymerizing vinyl pyrrolidone with vinyl esters are described in US. Patent 2,497,705, issued Feb. 14, 1950.

The ratio of vinyl alcohol to vinyl pyrrolidone in the copolymers used as emulsion binders within the scope of this invention may be varied widely depending upon the ultimate intended use to which the photosensitive emulsion is to be put, which intended use will in part determine the desired size of the silver halide crystals. As a general rule, the greater the ratio of vinyl alcohol to vinyl pyrrolidone in the copolymer, the larger the maximum size of silver halide crystals which may be grown therein. This phenomenon may readily be observed by referring to the accompanying drawings, wherein FIGS. 1 and 2 provide controls, being photomicrographs at a magnification of 40,000 of silver halide crystals grown in pure polyvinyl pyrrolidone and pure polyvinyl alcohol, respectively. As can readily be seen, the crystal size is exceedingly small, as a result of the behavior of these two homopolymers as crystal growth restrainers.

FIG. 3 is a photomicrograph at a magnification of 40,000 of a silver halide crystals grown in a copolymer binder comprising vinyl alcohol/vinyl pyrrolidone in a molar ratio of 36:64. As can readily be seen, the resulting silver halide crystals have a diameter of generally about 1.5 times that of crystals grown in either of the pure homopolymers.

FIGS. 4 and 5 (at a magnification of 40,000 and 6 (at a magnification of 10,000 are photomicrographs of silver halide crystals grown in copolymers of vinyl alcohol/vinyl pyrrolidone in rations of 57:43, 75:25, and 92:8, respectively; these illustrations are clearly demonstrative of the growth trends discussed above.

FIG. 6, showing an emulsion binder comprising a 92.8 vinyl alcohol/ vinyl pyrrolidone copolymer, warrants particular attention, particularly as compared with FIG. 2, in which the binder is pure polyvinyl alcohol. It can be seen that even a substitution of less than 10% of the hydroxyl groups on the polymer chain produces an enormous difference in the characteristics of the polymer as a photographic emulsion binder.

FIG. 7 (at a magnification of 10,000 further illustrates the unobviousness of the instant invention, in showing silver halide crystals grown in a binder consisting of a simple mixture of polyvinyl alcohol and polyvinyl pyrrolidone in a weight ratio of 70:30. As can be seen, there is substantially no difference in size between these crystals and those grown in the pure homopolymers. The illustration of FIG. 7 is best compared to that of FIG. 5, which shows approximately the same ratio of vinyl alcohol to vinyl pyrrolidone in a copolymer; the crystal diameter difference is both surprising and unexpected.

FIG. 8 (at a magnification of 10,000X) shows an emulsion binder comprising substantially the same copolymer as was used in the binder shown in FIG. 5. However, While in the emulsions of FIGS. 3-6, some gelatin or derivative thereof was added subsequent to silver halide crystal formation, the emulsion pictured in FIG. 8 is completely and totally devoid of gelatin in any form. It can be seen that the crystal diameter obtained in this emulsion is even greater than that of the crystals of FIG. 5. (This increase in crystal size will be dealt with in greater detail subsequently.) Thus, the various silver halide crystal sizes obtained may be summarized as follows:

Average crystal diameter,

Emulsion binder: millimicrons Pure polyvinyl pyrrolidone (PVP) (FIG. 1) Up to 75 Pure polyvinyl alcohol (PVA) (FIG. 2) Up to 50 36:64 VA/VP copolymer (FIG. 3) Up to 57:43 VA/VP copolymer (FIG. 4) Up to 200 75:25 VA/VP copolymer (FIG. 5) Up to 300 92:8 VA/VP copolymer (FIG. 6) Up to 500 70:30 PVA/PVP mixture (FIG. 7) Up to 50 The photomicrographs of FIGS. 1 through 8 were prepared by taking a small sample of each emulsion and diluting it with water. A drop from the diluted dispersion was placed on an electron microscope grid and dried. A carbon replica of the grid surface was made and was shadowed with chromium in accordance with well-known electron micrography techniques. The remaining polymer and silver halide grains were removed, and the replicated grid was photographed under the electron microscope.

FIGS. 1 through 8 are representative portions of .each photomicrograph so prepared; an approximate micron scale is indicated for each figure. The preparation of each of the emulsions of FIGS. 1 through 8 will be described in detail in the examples given hereinafter.

In addition to crystal size, certain other characteristics were found to vary somewhat with the ratio of vinyl alcohol to vinyl pyrrolidone in the copolymer emulsion binder, such as film speed and image density; these will be discussed in detail hereinafter. Other desirable characteristics were found to be possessed by all of the materials, such as latent image stability and the ability to be optically and chemically sensitized.

The following general procedure may be used for preparing photographic emulsions using as the sole colloid binder, vinyl alcohol/vinyl pyrrolidone copolymers:

Awater-soluble silver salt, such as silver nitrate, is reacted with at least one water-soluble halide, such as potassium, sodium or ammonium bromide, preferably together with potassium, sodium or ammonium iodide, in an aqueous solution of vinyl alcohol/ vinyl pyrrolidone. The dispersion of silver halide thus formed contains water-soluble salts, as a by-product of the double decomposition reaction, in addition to any unreacted excess of the initial salts. To remove these soluble materials, the dispersion is coagulated, such as by the addition of a nonsolvent liquid, e.g., acetone, and the coagulum is separated from the supernatant liquor and washed with water, or a mixture of water and nonsolvent if the latter is water-miscible.

An alternative procedure for removing the soluble salts is to add to the dispersion an acid-coagulable derivative of gelatin, such as gelatin derivatives of trimellitic acid anhydride; and then to lower the pH by the addition of a suitable acid, thereby bringing about precipitation and coagulation of the emulsion; the resulting emulsion is then washed with water. This procedure is described and claimed in US. Patent 3,118,766, issued Jan. 21, 1964, to Peter H. Roth. Additional procedures for providing acid-coagulable gelatin derivatives and employing such derivatives in the coagulation of silver halide emulsions are described in US Patents Nos. 2,614,928, issued Oct. 21, 1952; 2,614,929, issued Oct. 21, 1952; 2,728,662, issued Dec. 17, 1955; and 2,956,880, issued Oct. 18, 1960.

Alternatively, the dispersion may be coagulated by the incorporation of other specified additives, as disclosed in US. Patents Nos. 1,844,716, issued Feb. 9, 1932 (the salt-forming elements of Group IV of the Periodic Table); 2,489,341, issued Nov. 29, 1949 (anion soaps); 2,527,261, issued Oct. 24, 1950 (anion soaps); 2,527,268, issued Oct. 24, 1950 (anion soaps); and 2,618,556, issued Nov. 18, 1952 (ammonium salts, and salts of the alkali metals having an atomic weight less than 140).

When coagulation and washing of the dispersion is complete, the emulsion is after-ripened, preferably by adding either gelatin or an additional quantity of vinyl alcohol/ vinyl pyrrolidone copolymer, redissolving the emulsion, and heating the solution and adjusting the pH and pAg as desired. Also, at this point, any desired chemical sensitizing agent may be added. For example, the emulsions may be chemically sensitized with sulfur com pounds such as sodium thiosulfate or thiourea; with reducing substances such as stannous chloride; with salts of noble metals such as gold, rhodium, and platinum; with amines and polyamines; with quaternary ammonium compounds such as a-picolinium bromide; and with polyethylene glycols and derivatives thereof. Particularly good photographic results may be obtained where the chemical sensitizer is ammonium aurous thiocyanate, as described in US. Patent 2,399,083, issued Apr. 23, 1946.

The emulsions may also be optically sensitized with cyanine and merocyanine dyes, as described, for example, in US. Patents Nos. 1,846,301; 1,846,302; 1,942,854; 1,990,507; 2,112,140; 2,165,338; 2,493,747; 2,493,748; 2,503,776; 2,519,001; 2,666,761; 2,734,900; and 2,739,964.

Where desired, suitable antifoggants, restrainers, accelerators, preservatives, coating aids, and/or stabilizers may be included in the composition of the emulsion.

Following preparation as described above, the emulsions of this invention may be coated and processed according to conventional procedures known in the manufacturing art. They may be coated, for example, onto various types of rigid or flexible supports, such as, glass, paper, metal, and polymeric films of both the synthetic type and those derived from naturally occurring products. As examples of specific materials which may serve as supports, mention may be made of paper: aluminum; polymethacrylic acid; methyl and ethyl esters; vinyl chloride polymers; polyvinyl acetal; polyamides such as nylon; polyesters such as polymeric film derived from ethylene glycol-terephthalic acid; and cellulose derivatives such as cellulose acetate, triacetate, nitrate, propionate, butyrate, acetate-propionate, and acetatebutyrate.

The following nonlimiting examples illustrate the preparation of photosensitive emulsions in accordance with this invention. In each example, the following procedure was followed.

To 270 ml. of water were added 44 g. of ammonium bromide and 0.5 g. of potassium iodide. To this solution was added 4 g. of vinyl alcohol/vinyl pyrrolidone copolymer; when the copolymer had completely dissolved,

the solution was brought to 55 C. With continuous agitation, g. of a 10% by weight solution of silver nitrate in water was added to the polymer solution; after a two-minute pause, an additional 440 g. of the silver nitrate solution was added over a period of 22 minutes. Thereafter, the emulsion was ripened for 30 minutes at 55 C., with continuous agitation, at the end of which it was rapidly cooled to below 20 C.

Two alternate procedures were used to flocculate and wash the emulsion; both gave similar and satisfactory results in the ultimate photographic product:

(a) The emulsion was precipitated by the addition of acetone, and the resulting floc was washed with an acetone-water solution.

(b) 40 g. of gelatin, 10% derivatized with trimellitic acid anhydride, were added to the emulsion, after which precipitation was effected by lowering the pH of the solution to about 3.5 with sulfuric acid. The resulting floc was washed with distilled water.

When washing of the floc was complete by either of the above methods (as determined by supernate conductivity measurements), 18 g. of either gelatin or vinyl alcohol/vinyl pyrrolidone copolymer were added to the emulsion. The emulsion mixture was re-dissolved in water at 35 C.; the pH of the solution was adjusted to 5.70 and the pAg to 8.80. The temperature of the solution was then raised to 55 C., and 1 ml. of an aqueous ammonium aurous thiocyanate solution (containing 10 mg. of gold) and 2 ml. of an 0.02% aqueous solution of sodium thiosulfate were added. The resulting emulsion was ripened at 55 C. with continuous agitation; samples were taken every 30 minutes for photographic evaluation, and at the end of about minutes, a sample was taken for electron micrography.

In order to obtain preliminary photographic data for the novel emulsions of this invention, emulsion samples taken as indicated above were coated on a cellulose triacetate film base to a silver coverage of 250 mg. per square foot. The films so prepared were exposed on an Edgerton, Germeshausen & Grier, Inc., Mark IV sensitometer, and developed for five minutes at about 68 F. with a developer solution comprising DK-60A (tradename of Eastman Kodak Company, Rochester, N.Y., for a developer formulation comprising 2.5 g. p-methylaminophenol sulfate, 50 g. sodium sulfite, and 2.5 g. hydroquinone), 20 g. of Kodalk (trade name of Eastman Kodak Company, for an alkali comprising sodium metaborate, described in US. Patent No. 1,976,299), 0.5 g. of potassium bromide, and sufficient water to make one liter of solution. Thereafter, the films were short-stopped by contact for about 15 seconds at about 68 F. with a solution comprising 533 cc. of 28% acetic acid in 3.3 gallons of water, and were fixed by contact for five minutes in the dark followed by five minutes in the light at about 68 F. with an acid hardening fix solution comprising 240 C. sodium thiosulfate, 15 g. anhydrous sodium sulfite, 48 cc. of 28% acetic acid, 7.5 g. boric acid, 15 g. potassium alum, and sufiicient water to make one liter of solution. Finally, the films were washed with water, dried, and read on a Quantascan automatic recording densitometer Model 101-A.

Any change in the aforementioned procedure is noted in each example.

EXAMPLE 1 (control) An emulsion was prepared by the above procedure, but using pure polyvinyl pyrrolidone having an average molecular weight of about 100,000 (commercially available from General Aniline and Film Corporation) instead of a vinyl alcohol/vinyl pyrrolidone copolymer; the emulsion was precipitated by the derivatized gelatin procedure, and gelatin was added in the after-ripening step.

The following table summarizes the densitometer readings made on the sampler of this emulsion:

Speed is defined as the reciprocal of the number of meter-candleseconds required to give a density of 0.2 above fog, as measured on a manual-reading densitometer.

FIGURE 1 is a photomicrograph taken of a 180 minute emulsion sample. The silver halide crystal size is typical of that-obtained with synthetic materials in general, most of which are well known to behave as crystal growth restrainers. The small crystal size is believed to account, at least in part, for the very low photographic sensitivity.

EXAMPLE 2 (control) An emulsion was prepared by the above procedure, but using pure polyvinyl alcohol having an average molecular weight of about 100,000 (commercially available from E. I. du Pont de Ncmours & Co., Wilmington, Del., designated Type 7260) instead of a vinyl alcohol/ vinyl pyrrolidone copolymer. The procedure was performed through the washing stage, but the emulsion was not after-ripened because of its incompatibility with gelatin. However, a sample of the emulsion was used to prepare a photomicrograph (FIG. 2). As can readily be seen, silver halide crystal size was even smaller than that obtained in Example 1, with pure polyvinyl pyrrolidone.

EXAMPLE 3 A copolymer of vinyl alcohol/ vinyl pyrrolidone having a vinyl alcohol to vinyl pyrrolidone molar ratio of 25:75 was prepared by hydrolyzing 400 g. of the corresponding vinyl acetate/vinyl pyrrolidone copolymer (comprising 3 parts vinyl acetate to 7 parts vinyl pyrrolidone on a weight basis, and having an average molecular weight of about 100,000; designated E735 commercially available from General Aniline and Film Corporation, Antara Chemicals, 435 Hudson Street, New York, N.Y.) in methanol, with 10 g. of sodium methoxide. The reaction was allowed to proceed until the ester grouping of the vinyl acetate was no longer observed in the infrared spectrum of an aliquot portion. The copolymer was then neutralized with dilute acetic acid, and precipitated and washed with a 50/50 acetone-ether mixture; finally, it was ground and dried.

An emulsion was prepared as described previously using 4 g. of the copolymer prepared as just described; the emulsion was precipitated by the derivatized gelatin procedure, and gelatin was added in the after-ripening step.

The following table summarizes the densitometer readings made on the samples of this emulsion:

* Same as in Table 1.

FIG. 3 is a photomicrograph taken of a 180 minute emulsion sample. It will be readily observed that the average crystal diameter is considerably larger than that obtained with either homopolymer.

EXAMPLE 4 A copolymer of vinyl alcohol/ vinyl pyrrolidone having a vinyl alcohol to vinyl pyrrolidone molar ratio of 57:43 was prepared by hydrolyzing a solution of 400 g. of the corresponding vinyl acetate/vinyl pyrrolidone copolymer (comprising one part vinyl acetate to one part vinyl pyrrolidone on a weight basis and having an average molecular weight of about 100,000; designated E535 commercially available from General Aniline and Film Corporation) in methanol, with 10 g. of sodium methoxide, until the ester groups were unobservable on infrared analysis. The product was precipitated into acetone, ground, and dried.

An emulsion was prepared exactly as in Example 3, using 4 g. of the copolymer prepared as just described. The following table summarizes the densitometer readings made on the emulsion samples:

TABLE 3 Sampling Times Dmnx I)miu- Speed Gamma 30 minutes 1. 76 0. 02 1. 8 1. 10 60 minutes 1.99 0.02 2.0 1.21 00 minutes. 2.05 0.04 2. 2 1. 23 minutes. 2. 09 0. O4 2. 4 1. 26 minutes. 2.08 0. 04 2. 4 1.20 minutes 2. 35 0. 08 2. 4 1. 34

* Same as in Table 1.

TABLE 4 Interval between exposure and development mux. D", in. Speed G amma 0 hours 2. 41 0.03 2. 3 1. 54 6 hours 2. 30 0. 07 2. 4 1. 45 24 hours 2. 66 0.07 2. 5 1.65 48 hours 2. 59 0. 09 2. 8 1. 57

*Same as in Table l.

The results of this test bear witness to the high degree of latent image stability which is characteristic of the novel emulsions of this invention. While there was s me increase in fog (D as a function of time, it is believed that this was the result of accelerated aging of the emulsion because of the fact that it was not stabilized. It will be obvious that this deficit is readily correctable by the use of any of the emulsion stabilize-rs which are commonly used in the photographic art.

FIG. 4 is a photomicrograph taken of a 180 minute emulsion sample. A substantial increase in the diameter of the silver halide crystals, even as compared with the emulsion of Example 3 and FIG. 3 is readily observable.

EXAMPLE 5 A copolymer of vinyl alcohol/ vinyl pyrrolidone having a vinyl alcohol to vinyl pyrrolidone molar ratio of 75 :25 was prepared by hydrolyzing 400 g. of the corresponding vinyl acetate/ vinyl pyrrolidone copolymer (comprising 7 parts vinyl acetate to 3 parts vinyl pyrrolidone on a weight basis, and having an average molecular weight of about 50,000; designated E335, commercially available from General Aniline and Film Corporation) with 10 g. of sodium methoxide in methanol until the ester groups were unobservable on infrared analysis. The resulting polymer was precipitated into acetone, ground, and dried.

An emulsion was prepared exactly as in Example 3, using 4 g. of the copolymer prepared as just described. The following table summarizes the densitometer readings made on the emulsion samples:

*Same as in Table 1.

A latent image fading test was performed on 180 minute samples of this emulsion following the procedure given in Example 4; the results are summarized in the following table:

*Same as in Table 1.

FIG. 5 is a photomicrograph of 180 minute emulsion sample. The crystal diameter is excellent.

EXAMPLE 6 lation, 18 g. of the same copolymer as used in the emul- 2 sion itself, rather than gelatin, was added in the afterripening procedure. The following table summarizes the densitometer readings on samples of this emulsion:

TABLE 7 Sampling Times Dmax, Dmin Speed* Gamma 120 minutes 1. 96 0. 23 23 0. 80 150 minutes 1. 90 0. 26 21 0. 82

*Same as in Table 1.

It will be noted that in Table 7, the D and speed were considerably higher than those of corresponding samples in Table 5, even though both sets of emulsions were based on the same copolymer. This increase is believed to be attributable primarily to the higher preparation and ripening temperature in the samples for the former table. The higher temperature resulted in greater crystal growth and correspondingly higher speed. It should be, noted, however, that this same principle could not be applied tothe samples reported in Table 5, owing to the inclusion of gelatin in the after-ripening procedure; where suchemulsions were ripened at temperatures which much exceeded 55 C., the grain size became too large, resulting in acomparatively high D (fog).

EXAMPLE 7 A copolymer of vinyl alcohol/vinyl pyrrolidone having a vinyl alcohol to vinyl pyrrolidone molar ratio of 92:8 was prepared, by hydrolyzing 450 g. of the corresponding vinyl acetate/ vinyl pyrrolidone copolymer, having a vinyl acetate to vinyl pyrrolidone ratio of 9:1 on a weight basisgand having an average molecular weight of about 100,000. The starting material was obtained as a tolueneethyl acetate solution from General Aniline and Film Corporation, Dyestuff and Chemical Division, 435 Hudson Street,New York, N.Y., and is commercially designated Kolinia 10. The solid vinyl acetate/ vinyl pyrrolidone copolymer was obtained by precipitation of the commercial solution into hexane. The solid was .then dissolved in hot ethanol and hydrolyzed with sodium ethoxide; the dcsired vinyl alcohol/vinyl pyrrolidone copolymer rapidly TABLE 8 53 111911118 Times Dmnx Dmin. Speed Gamma v 30 miuutes** 1. 48 0.27 30 0. 61 60 rninutes** l. 41 0. 33 50 0. 54 minutes 2. 10 0. 59 39 0. 81 minutes 2.20 0. 73 33 0.73

*Same as in Table 1.

Din. was higher than the value indicated, but the exposure given was too short in duration and/0r too low in intensity to develop the full density of the negative.

The processed samples appeared fairly grainy and seemed to give a rather high fog, as indicated in Table 8 by the D readings. This is believed to be caused by a tendency toward agglomeration of the crystals, owing to the high (over 90%) concentration of polyvinyl alcohol and its known incompatibility with gelatin. In the pH ranges employed in the processing of the emulsions of this invention, it is well known that mixtures of pure polyvinyl alcohol and gelatin result in complete agglomeration. Accordingly, where vinyl alcohol/ vinyl pyrrolidone copolymers having a vinyl alcohol content of about 90% or more are used as emulsion binders in accordance with this invention, it is preferred that after ripening of the emulsion be carried out using additional copolymer (as described in Example 6) rather than with gelatin; moreover, in some cases it will be desirable to achieve flocculation of the emulsion by any of the various procedures which do not involve the use of gelatin. As will be seen by a comparison of the results of this example with those reported in Example 5, where lesser amounts (e.g., only about 75%) of the copolymer comprise polyvinyl alcohol, there appears to be no problem with gelatin compatibility.

To further illustrate the unobviousness of this invention, attempts were made to prepare a photographic emulsion using a simple mixture of polyvinyl alcohol and polyvinyl pyrrolidone, rather than a copolymer. The following example is an illustration of one such attempt.

EXAMPLE 8 An emulsion was prepared by the basic procedure, but using a mixture of 2.8 g. of the same polyvinyl alcohol as was used in Example 2, and 1.2 g. of the same polyvinyl pyrrolidone as was used in Example 1, for a total of 4 g. of polymer. The emulsion was precipitated by the derivatized gelatin procedure; the process was carried only through the washing stage, as in Example 2. FIG. 7 is an electron micrograph made of an emulsion so prepared. As is readily seen, the crystal diameters are similar to those obtained with either of the pure homopolymers.

Emulsions prepared in accordance with this invention may be employed in virtually any photographic system in which gelatino-silver halide emulsions have been employed heretofore. Of particular interest, is their use in diffusion transfer processes, wherein an exposed photosensitive silver halide emulsion is developed and, substantially concurrently therewith, diffusible image-forming components are obtained according to the point-to-point degree of exposure of the emulsion. These diffusible image-forming components are transferred, in solution, from the emulsion to a suitable print-receiving layer to provide thereto the desired image formation.

In one type of diffusion transfer process, for the formation of silver images, a latent image contained in an exposed silver halide emulsion is developed and, almost concurrently therewith, a soluble silver complex is obtained by the action of a silver halide solvent upon undeveloped silver halide of said emulsions. According to one mechanism, the photosensitive silver halide emulsion is developed with a viscous processing composition spread between the protosensitive element comprising the silver halide emulsion and an image-receiving element comprising a suitable silver precipitating layer. The processing composition effects development of the latent image in the emulsion and, substantially contemporaneous therewith, forms a soluble silver complex, for example, a thiosulfate or thiocyanate complex, with undeveloped silver halide. This soluble complex is, at least in part, transferred in the direction of the image-receiving element and the silver thereof is for the most part precipitated in the silver precipitating layer of the element to form an image therein.

The following example illustrates the use of an emulsion of this invention in a silver diffusion photographic process.

EXAMPLE 9 An emulsion was prepared as described in Example 6, except that instead of the derivatized gelatin flocculation procedure, the emulsion was precipitated by the addition of acetone, and was thereafter washed with a 50:50 water-acetone solution. FIG. 8 is a photomicrograph made of a 180 minute emulsion sample; it will be observed that the average crystal diameter somewhat larger than that of the crystals in FIG. (Example 5), wherein the same copolymer was employed but was flocculated with derivatized gelatin, and gelatin was added in the after-ripening step. (The reasons for this diameter increase were discussed in Example 6.)

A 120-minute sample of the emulsion prepared as described above was coated on a paper base, and was exposed and processed with a processing solution and an image-receiving element from a Polaroid 3000 Speed Land Film Pack, Type 107 film assembly; the negative and image-receiving element were maintained in superposed position for 15 seconds, after which they were stripped apart. The photographic characteristics of the resulting positive print were measured on a densitometer; the readings obtained are as follows:

1 Speed in this instance is defined as 4 divided by the exposure in meter-candle-seconds at the point on the positive characteristic curve (i.e., the curve obtained by plotting the reflection density of the positive image as a function of the gggoegiosure of the negative) which corresponds to a denslty Additive color reproduction may be produced by exposing a photosensitive silver halide emulsion through an additive color screen having filter media or screen elements each of an individual additive color such as red or blue or green, and by viewing the reversed or positive silver image, formed by transfer to a transparent image receiving element, through the same or a similar screen which is suitably registered with the positive image carried by the image-receiving layer.

U.S. Patent No. 2,983,606, issued May 9, 1961, discloses and claims diffusion transfer processes wherein initially mobile anddiffusible dye developers, that is, complete dyes which contain in the same molecular structure a silver halide developing function, are utilized in the development of an exposed photosensitive silver halide emulsion, effecting thereby immobilization of the dye developers in the photosensitive emulsion, as a function of the point-to-point degree of exposure thereof, and transferring, at least in part, the resultant imagewise distribution of mobile dye developer from unexposed areas of the photosensitive emulsion, by imbibition, to a superposed image-receiving layer or element, to impart thereto a subtractive color transfer image.

US. Patents Nos. 2,647,049, issued July 28, 1953; 2,661,293, issued Dec. 1, 1953; 2,698,244, issued Dec. 28, 1954; 2,698,798, issued Jan. 4, 1955; and 2,802,735, issued Aug. 13, 1957, disclose diffusion transfer processes wherein color coupling techniques are utilized to provide subtractive color image. Image-forming components comprising one or more color developing agents and one or more color formers or couplers are reacted to provide color image formation to a superposed image-receiving element.

As was indicated above, vinyl alcohol/ vinyl pyrrolidone copolymer photosensitive emulsions can be optically sensitized with virtually any of the many well-known sensitizing agents.

The following example is an illustration of the optical sensitization of one such material.

EXAMPLE 10 An emulsion prepared as in Example 6 and afterripened for about minutes was spectrally sensitized to extend its light response to 650 millimicrons. This was accomplished by adding 1.6 ml. of an 0.1% methanol solution of 3,3'-bis-(6-sulfobutyl)-5,5'-dichloro-9-methylthiacarboxyanine betaine, a symmetrical benzothiazole carbocyanine sensitizing dye, per gram of silver in the emulsion. The addition was carried out over a period of 15 minutes with constant stirring at 35 C. FIG. 9 shows the resulting wedge spectrogram, as determined on a variable exposure grading spectrograph.

In the foregoing description, the photosensitive emul sion binders generally consisted essentially entirely of vinyl alcohol/vinyl pyrrolidone copolymer; the only gelatin present was added after silver halide growth had been substantially completed, either during the flocculation procedure, or during the after-ripening step to confer chemical sensitivity on the emulsion. And, as was clearly demonstrated, all of this gelatin can be replaced by the copolymer. However, in certain photographic applications, it may be desirable to replace part, but not all, of the gelatin in the photosensitive emulsion. In view of the characteristics of vinyl alcohol/vinyl pyrrolidone copolymers described above, and further, in view of their compatibility with gelatin in substantially all proportions, it will be obvious that these copolymers are ideally suited for such Work. Or, if desired, any of the conventional bulk-increasing materials well known to the photographic art may also be incorporated into the emulsions of this invention.

Emulsions made with vinyl alcohol/vinyl pyrrolidone copolymers exhibit a strong tendency toward water solubility. For some photographic processes, such as diffusion transfer processes, this poses no particular problem; indeed, for certain applications it may prove to be advantageous. However, where it is desired to provide a relatively water-insoluble emulsion, as would be needed, for example, for conventional tank-type development, it will be obvious that conventional cross-linking agents, such as vinyl sulfones, chromium salts, boric acid, borates, aldehydes, such as glyoxal or succinaldehyde, and the like, may be added during the emulsion synthesis at any time subsequent to silver halide crystal formation.

An alternative procedure for rendering the emulsions of this invention suitable for tank-type development without introducing additional cross-linking agents as described above and at the same time avoiding the addition of gelatin in any form to the composition (as Was done in Examples 3-7 and 9) is to incorporate a synthetic material which is compatible with the vinyl alcohol/vinyl pyrrolidone copolymer and which is of a nature such that it is readily hardened by the reagents commonly employed in photographic processing, such as the acid hardening fix solution used for the above examples and described previously. The following example illustrates such an embodiment.

EXAMPLE 11 An emulsion was prepared as described in Example 9. Following a ripening period of about 120 minutes, a sample was removed and a quantity of high molecular weight polyvinyl alcohol (Type 72-60, Du Pont) equal to the amount of copolymer in the sample was added. Thereafter, the resulting emulsion was coated on a polyvinyl alcohol-subcoated cellulose acetate butyrate film, and was exposed and developed by the procedure previ- 13 ously described. The densitomer readings made on the sample are as follows:

1 Same as in Table 1.

The negative was characterized by good mechanical properties subsequent to development; the negative image was noted to be sharp and clear.

The term photosensitive and other terms of similar import are herein employed in the generic sense to describe materials possessing physical and chemical properties which enable them to form usable images when photoexposed by radiation.

Since certain changes may be made in the above products and processes without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying illustrations shall be interpreted as illustrative and not in a limimting sense.

What is claimed is:

1. A photosensitive silver halide emulsion wherein the emulsion binder comprises a copolymer of vinyl alcohol and vinyl pyrrolidone.

2. The product of claim 1 wherein substantially all of said emulsion binder consists of a copolymer of vinyl alcohol and vinyl pyrrolidone.

3. The product of claim 1 wherein said silver halide emulsion is a silver iodobromide emulsion.

4. The product of claim 1 wherein said emulsion includes at least one chemical sensitizing agent.

5. The product of claim 1 wherein said emulsion includes at least one optical sensitizing agent.

6. The product of claim 1 wherein said copolymer of vinyl alcohol and vinyl pyrrolidone has a molecular weight range of from about 20,000 to 300,000.

7. The product of claim 1 wherein said copolymer of vinyl alcohol and vinyl pyrrolidone has a molar ratio of 36 parts vinyl alcohol to 64 parts vinyl pyrrolidone.

8. The product of claim 1 wherein said copolymer of vinyl alcohol and vinyl pyrrolidone has a molar ratio of 57 parts vinyl alcohol to 43 parts vinyl pyrrolidone.

9. The product of claim 1 wherein said copolymer of vinyl alcohol and vinyl pyrrolidone has a molar ratio of 75 parts vinyl alcohol to 25 parts vinyl pyrrolidone.

10. The product of claim 1 wherein said copolymer of vinyl alcohol and vinyl pyrrolidone has a molar ratio of 92 parts vinyl alcohol to 8 parts vinyl pyrrolidone.

References Cited FOREIGN PATENTS 1,005,404 9/1965 Great Britain.

NORMAN G. TORCHIN, Primary Examiner R. LYON, Assistant Examiner 

